1. Field of the Invention
The present invention relates to a printing apparatus for ejecting ink on a printing medium from a print head supplied with ink through a tapered ink supply needle, and more particularly to an ink cartridge and an ink supply system removably attached to the printing apparatus.
2. Description of the Related Art
Typically, an ink cartridge having a supply port for providing ink is connected to a print head of a printing apparatus for ejecting ink on a printing medium from nozzle aperture of the print head The printing apparatus has a hollow ink supply needle in the ink supply channel to supply ink to the print head. When the ink cartridge is mounted on the printing apparatus, the hollow ink supply needle is inserted into the ink supply port of the ink cartridge so that ink is introduced to the print head.
When the ink cartridge includes a porous member within its ink chamber for absorbing ink, the ink chamber is depressurized by the porous member. Therefore, the ink cartridge needs to be sealed so as not to undesirably suck air or bubbles in the ink chamber.
FIG. 27 is a cross sectional view of an example of an ink cartridge and an ink supply channel. The ink cartridge 112 has an ink supply port 114 and a packing member 120 contained in the ink supply port 114 and fitting with an ink supply needle 113 which is connected to a print head 116. The ink supply port 114 is sealed with a sealing film, not shown in the drawings, prior to use. When the ink supply needle 118 is inserted in the ink supply port 114 and fitted in the packing member 120, the ink supply needle 118 penetrates the sealing film. Ink is then provided to the print head 116 via the ink supply needle 118. The ink cartridge 112 is sealed by fitting the ink supply needle 118 with the packing member 120.
When the ink cartridge 112 is removed from the printing apparatus with ink left therein, the sealing of the ink supply needle 118 with the packing member 120 is released. The result is that ink leaks from the ink supply port 114 or that air or a bubble enters the ink supply port 114. This means that a user of the ink cartridge cannot remove the ink cartridge until ink in the ink cartridge is completely used up. The user cannot repeatedly exchange a plurality of ink cartridges with his choice while ink still remains in the ink cartridge.
There has been provided an ink cartridge as disclosed, for example, in U.S. Pat. No. 5,777,646, having an elastic slit wall formed at an opening of an ink supply port and a ball slidably received in the ink supply port which is always urged against the elastic slit wall by a spring.
An ink supply channel of the conventional ink cartridge described above is opened by urging the ball with a hollow ink supply needle of the printing apparatus when the ink cartridge is mounted on the apparatus. The ink supply channel of the ink cartridge is closed when the hollow ink supply needle is removed from elastic slit wall because of the elastic force of the spring which always urges the ball against the elastic slit wall of the ink supply port. Therefore, ink does not leak from the ink supply port and air or bubble does not enter the ink supply port.
The conventional ink cartridge, however, has a drawback that the structure of the ink supply port is complicated as shown in FIG. 27. Therefore, the workability of the ink cartridge is deteriorated, and the manufacturing cost would rise up.
FIG. 28 shows another example of a conventional ink cartridge disclosed in Japanese patent application No. 5-229137 employing a packing member, or a rubber member disposed in the ink supply port and a ball which is urged against the packing member by a spring. Ink is supplied from an ink chamber to a print head via a cylindrical connecting means. The ball is urged by the cylindrical connecting means to move away from the packing member against the elastic force of the spring.
The ink cartridge illustrated in FIG. 28 has a packing member 134 disposed in the ink supply port 132 and a ball 136 abutting against the packing member 134 by means of an elastic force of a spring 138.
In the conventional ink cartridge 130 shown and FIG. 28, the packing member 134 serves as a valve seat sealing the ink supply port 132 with the connecting means, and the ball 136 serves as a valve body closing the ink supply port 132 in cooperation with the packing member 134. However, the relative position between the ball 136 and the spring 138 is unstable. This may cause an undesirable insufficient sealing by the ball 136 with the packing member 134. Furthermore, the connecting means needs to have a large contact area to sufficiently urge the ball 136 against the elastic force of the spring. Therefore, the connecting means is not easily inserted in the packing member 134. Furthermore, because the ball 136 is always urged toward the packing member 134 by the spring, the through hole of the packing member 134 may be expanded. This is disadvantageous because it may cause an insufficient connection between the ball 136 and the packing member 134.